1. Field of the Invention
The present invention relates generally to lighting systems. More particularly, the present invention relates to a sequencer for a remotely illuminated lighting system, and a method of producing a sequenced light pattern.
2. Discussion of the Related Art
Airports incorporate a system of lighting to provide guidance to approaching aircraft. The conventional aircraft approach lighting system (ALS) includes groups of incandescent lamps distributed over a field, lighting several thousand feet of the approach to the runway within specific requirements for angular light distribution, color and intensity. One aspect of the ALS is a series of lights extending along the centerline of the runway that are illuminated in sequence to guide an approaching aircraft along the landing path. Such sequentially illuminated light series are often referred to as "rabbit" lights.
The rabbit lights used in the ALS are typically high intensity incandescent lamps. A mechanical switching system or an electronic controller typically controls a flow of current to each of the lamps for illumination in the desired sequence. The mechanical switching system uses mechanical switches and a switch actuator mechanism, such as a rotating camshaft, to sequentially close the switches. As the switches close, an electric circuit is completed allowing current to flow to an associated lamp. Electro-mechanical relays can replace the mechanical switches. Selective application of current to the relay coil causes opening and closing of the relay contacts for completing the electric circuit. A suitable programmable logic controller, or other control device, may be used to provide the sequenced relay coil currents. In an entirely electronic controller, high-current capacity switching transistors are used to couple current to the lamps in the appropriate sequence.
The mechanical switching systems, including those based upon electromechanical relays, suffer from an increased incidence for maintenance. The switch contacts are prone to wear that must be monitored, and at the appropriate time the contacts must be replaced. Electronic controllers are expensive, and have substantial cooling requirements for the high-current capacity transistors. An additional problem with the use of incandescent lamps in the ALS rabbit lighting system lies with monitoring the many light sources, i.e., each incandescent lamp, for failure. The availability of the ALS is dependent on the number and location of failed lamps in the system. Existing monitoring systems rely on observed lamp currents to infer if a lamp is operating properly. Many factors, including the condition of the contacts and the age of the lamp may effect these current readings resulting in false readings and false indications of lamp failure. Replacing failed lamps is a significant cost owing to the required human and equipment resources and the cost of the lamps. Additionally, diagnosis of lamp failure is not limited to the lamp itself but must also include diagnosis of the mechanical switching system or electronic controller thereby adding time and cost to the maintenance process.
Other applications of sequentially illuminated lighting systems include aerial obstruction lighting systems, road hazard lighting systems, building signage, and the like. Similar to the ALS rabbit lighting system, these systems too rely on a distributed network of incandescent lamps. Failure of an obstruction beacon atop a radio tower can have disastrous consequences for aircraft operating in the area. Replacing failed lamps is not a simple operation, and is certainly not for the faint of heart, as a technician is typically required to scale the tower structure to access the lamp for replacement.
Thus there is a need for a sequencing system that does not rely on mechanical switching and/or electronic switching for generating a light sequence pattern. Additionally, here is a need for a sequenced light system that overcomes the limitations of sequenced light systems relying on a distributed network of incandescent lamps as light sources.